As angry, sometimes violent protests stretched into a ninth day in the St. Louis suburb of Ferguson, Missouri Gov. Jay Nixon played his highest-value executive card — activating the state's National Guard.

Authorities have tried unsuccessfully to quell the nighttime violence that erupted Aug. 9 in Ferguson after Officer Darren Wilson, 28, who is white, fatally shot unarmed black pedestrian Michael Brown, 18. They beefed up the police presence and imposed a curfew. They tear-gassed unruly protesters and fired rubber bullets. On Saturday, Nixon declared a state of emergency, laying the foundation for his executive order Monday that called up the National Guard.

Governors often turn to their guardsmen and women in emergencies: floods, hurricanes, tornadoes and other catastrophes. Nixon last deployed his National Guard a year ago, on Aug. 7, 2013, in response to flash floods in southern Missouri.

Hawaii's National Guard deployed last week to provide security on the Big Island after Hurricane Iselle left communities without electricity. During President Obama's 2009 inauguration, 10,000 National Guard soldiers from all over the country deployed to Washington, D.C., where they were deputized by the city police department to help with security. During Hurricane Katrina, Guard soldiers assisted with search and rescue and patrolled the city to prevent looting.

In those cases, as in Missouri now, the guard was activated by the state's governor to perform law enforcement duties.

More rare is a federal call-up by the president for a domestic mission.

The last time the Guard was federalized for a civil disturbance was in 1992 during the riots in Los Angeles that followed acquittal of the police officers charged with beating Rodney King, National Guard spokesman Rick Breitenfeldt said.

Nixon said he issued the order Monday after peaceful protests and prayer meetings on Sunday turned violent. He said protesters shot at police officers, looted businesses, threw Molotov cocktails, blocked roads and attempted to overrun the city's command center. He said the National Guard's mission will be limited to protecting the command center that was attacked Sunday night.

"As long as there are vandals and looters and threats to the people and property of Ferguson, we must take action to protect our citizens," Nixon said in a written statement.

The National Guard will coordinate with Col. Ron Replogle, superintendent of the Missouri State Highway Patrol, to restore order in the community, Nixon said. The order gives the National Guard the authority to take all necessary measures, including closing streets, to restore the peace.

The family of Michael Brown, the unarmed teen shot and killed by a police officer, had a private autopsy conducted on their son. Their lawyers say it confirms multiple witness reports. Pathologists say there are still a lot of unknowns.

"We have well-trained and well-seasoned soldiers" who have the equipment and resources for the mission, Missouri National Guard Brig. Gen.Gregory Mason said.

The measures taken by local police and state authorities have been criticized by civil liberties groups who say the actions to restore order have trampled First Amendment rights.

The American Civil Liberties Union said Nixon overrode constitutional rights of assembly and free speech when he declared a state of emergency Saturday and when the city instituted a curfew.

"The suspension of constitutional rights in Ferguson does much more than suppress speech. It subjects an entire community to imprisonment in their homes," the ACLU said in a written statement.

People in Ferguson "want to know where they can stand and raise their voices without fearing arrest or military-style assault," the statement said.